This invention relates to a sound field control device for imparting a sound field effect in reproduction of a music by an audio device and, more particularly, to a sound field control device capable of creating a stereophonic sound field with only a pair of loudspeakers.
Imparting of a sound field effect to a music reproduced is sometimes required as a high degree function for musical reproduction. The sound field effect herein means an effect which imparts presence to a listener in a narrow listening room as if the listener was listening to the music in a different space such as a concert hall. In the past, the sound field effect was realized by disposing at least four auxiliary loudspeakers about a room where the sound field effect is to be imparted and reproducing reflected sound signals of different directions produced on the basis of a source signal from these auxiliary loudspeakers.
A prior art system for imparting a sound field effect in reproduction of a music is shown in FIG. 2. In the system of FIG. 2, left and right 2-channel source signals L and R provided by a source device 10 are applied to a sound field control device 16 through input terminals 12 and 14. The sound field control device 16 is constructed in the form of a stereophonic pre-main amplifier having sound field effect imparting function and supplies the input source signals to output terminals 24 and 26 connected to main loudspeakers 84 and 86 through a pre-amplifier 18 and power amplifiers 20 and 22.
The source signals L and R are applied also to a reflected sound signal generation section (sound field effect processor) 28. For reproducing, by these four or more loudspeakers disposed about a listening point in a room, a multiplicity of reflected sounds which are produced naturally in a sound space such as a concert hall or a model space simulating such sound space on the basis of reflected sound data obtained in correspondence to each of hypothetical sound source positions of the reflected sounds in such sound space, the reflected sound signal generation section 28 stores impulse response characteristics of reflected sounds to be sounded by these loudspeakers as reflected sound parameters, generates reflected sound signals, i.e., signals of a multiplicity of reflected sounds to sounded by these loudspeakers by subjecting the respective stored reflected sound signal parameters to a convolution operation with a common source signal, and imparts a sound field effect by supplying these reflected sound signals to corresponding ones of the loudspeakers. This sound field effect imparting system is disclosed in detail in U.S. Pat. No. 5,027,687. More specifically, the source signals L and R applied to the reflected sound signal generation section 28 are synthesized to a single channel signal L-R or L+by a mixer 30. The single channel source signal L-R or L+R is converted to a digital signal by an analog-to-digital converter 34 through a low-pass filter 32 which is provided for eliminating an aliasing noise occurring in the analog-to-digital conversion. The digital source signal is then distributed to four channels and supplied to digital filters 36, 38, 40 and 42 of the respective channels for imparting the source signals with frequency characteristics. Source signals provided by the digital filters 36, 38, 40 and 42 are applied to reflected sound generation circuits 44, 46, 48 and 50 of the respective channels.
A read-only memory (ROM) 52 stores, as parameters of various sound field effect modes, reflected sound parameters of different directions in various sound spaces (such as a concert hall, a studio, a jazz club, a church and a karaoke room) which parameters are composed of delay time data and gain data as shown, for example, in FIG. 3. The reflected sound generation circuits 44, 46, 48 and 50 generate reflected sound signals for the source signal for the respective channels by performing a convolution operation with the source signal on the basis of a parameter of selected mode among the reflected sound parameters stored in the ROM 52. The reflected sound signals thus generated are converted to analog signals on a time shared basis by a digital-to-analog converter 54. An output signal of the digital-to-analog converter 54 is distributed to the respective channels and smoothed by low-pass filters 56, 58, 60 and 62 and then delivered out of the reflected sound signal generation section 28 as analog signals. The reflected sound signals of the respective channels, i.e., front left (FL), front right (FR), rear left (RL) and rear right (RR), are supplied to output terminals 72, 74, 76 and 78 connected to auxiliary loudspeakers 88, 86, 92 and 94 through power amplifiers 64, 66, 68 and 70.
Main signals L and R of the left and right channels provided by the sound field control device 16 are supplied to main loudspeakers 84 and 86 disposed in front of a listening point 82 in a listening room 80. The four channel reflected sound signals FL, FR, RL and RR are supplied to the auxiliary loudspeakers 88, 90, 92 and 94 disposed at four corners of the listening room 80. By this arrangement, a listener can enjoy a music reproduced in an acoustic space as if the listener was listening to the music in a real acoustic space.
In the above described prior art sound field control device, at least four loudspeakers are required for imparting a desired sound field effect.
It is an object of the invention to provide a sound field control device capable of imparting a sound field effect with two loudspeakers.